CTYPE(3) Library Functions Manual CTYPE(3)
isalpha, isupper, islower, isdigit, isalnum, isspace, ispunct, isprint,
iscntrl, isascii - character classification macros
. . .
These macros classify ASCII-coded integer values by table lookup. Each
is a predicate returning nonzero for true, zero for false. Isascii is
defined on all integer values; the rest are defined only where isascii
is true and on the single non-ASCII value EOF (see stdio(3S)).
isalpha c is a letter
isupper c is an upper case letter
islower c is a lower case letter
isdigit c is a digit
isalnum c is an alphanumeric character
isspace c is a space, tab, carriage return, newline, or formfeed
ispunct c is a punctuation character (neither control nor
isprint c is a printing character, code 040(8) (space) through
iscntrl c is a delete character (0177) or ordinary control char-
acter (less than 040).
isascii c is an ASCII character, code less than 0200
25 February 1983 CTYPE(3)